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theses

To achieve smooth motor performance in a rich and changing sensory environment, motor outputs must be constantly updated in response to sensory feedback. Although proprioception and cutaneous information are known to modulate motor output, it is unclear how they work together in the spinal cord to shape rhythmic motor actions, such as locomotion. Here we identify the medial deep dorsal horn (mDDH) as the epicenter for convergent proprioceptive and cutaneous information, recruited during walking. Within this zone of convergence we find that inhibitory neurons are particularly recruited, likely due to increased excitability and sensitivity to sensory input. To study inhibitory neurons in this region, we target a large group of glycinergic mDDH interneurons identified by their expression of parvalbumin (dPVs). dPV electrophysiological and morphological properties demonstrate recruitment during locomotion, role in sensorimotor processing, and high-gain, faithful encoding of sensory input. In support of a role in sensorimotor processing, we identify dPVs as a node for multimodal convergence (proprioceptive, cutaneous and cortical input) and output divergence, inhibiting diverse motor and premotor neurons. We demonstrate that the temporal dynamics of dPV activity is shaped by activation of sensory inputs; reducing spike timing variability and promoting oscillatory- like activity. We therefore propose that sensory-evoked activity in dPVs set the timing of output targets. To test this hypothesis, we devise a genetic strategy for specific ablation of dPVs. Electromyogram muscle recordings reveal that dPV ablation results in faster sensory- evoked muscle response, due to loss of dPV inhibition. dPV ablation does not change mice corrective reflexes. However, we observe phase- and speed-dependent changes to stride duration, frequency, interlimb coordination, gait transitions, and joint angles during treadmill walk. Together, our data suggest that convergent sensory inputs work in concert to coordinate the activity of dPVs, and in-turn regulate motor output in a contextually relevant manner.

http://dissertations.umi.com/gsnb.rutgers:12325

Ph.D.

Includes bibliographical references

doi:10.7282/t3-2h60-3p65

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